Power monitoring system

ABSTRACT

A power monitoring system with multiple current sensors.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a power monitoring system.

[0002] Referring to FIG. 1, many electrical power distribution systemsinclude a panel enclosure 10 into which is provided electrical powerusing one or more sets of wires 12. The electrical power may have anyvoltage, any current, and any number of phases (e.g., single phase, twophases, or three phases). Each phase of the electrical power to thepower panel is normally provided to a separate bus bar 14 a, 14 b, and14 c, which are normally elongate conductors within the power panel 10.A plurality of circuit breakers 16 a, 16 b, 16 c, etc., which trip orotherwise selectively disconnect electrical power, are electricallyinterconnected between one or more of the bus bars 14 a, 14 b, and 14 c,and respective loads 18 external to the power panel 10. In many powerpanels 10 the circuit breakers 16 are vertically aligned in one or morestrips 20 and 22. When the load 18 interconnected to a respectivecircuit breaker 16 within the power panel 10 draws excessive electricalcurrent then the circuit break 16 trips or otherwise disconnects theelectrical power to the load 18. In this manner, if a load shorts andthereafter draws excessive current then the circuit breaker will trip.Frequently, the load will be a three-phase load having three wiresprovided thereto, with one or more corresponding circuit breakers.

[0003] In many business environments a set of electrical loads, such asmotors, lighting, heating units, cooling units, machinery, etc., may beelectrically interconnected to one or more circuits, each of which maybe a single phase or multi-phase. Obtaining the total power usage of thebusiness may be readily obtained by reading the power meter provided bythe power utility. The power meter is normally electricallyinterconnected between the power panel and the power utility. In manycircumstances, it is desirable to monitor the power consumption ofindividual loads or groups of loads. The use of power meters permitseffective monitoring of the power consumption of particular loads. Also,a set of power meters permits effective sub-metering of different loads,buildings, or groups of loads to attribute and monitor the power usageof the business. For example, the power sub-metering may be used toattribute the power costs charged by the utility to different buildings,departments, or cost centers. The traditional approach to monitoringsuch power usage is to install a power meter at a location proximate theload itself. To install a typical power meter on a three phase load, acurrent sensor is located around each wire of the three phases and avoltage connection is electrically interconnected to each wire. Such apower meter is available from Veris Industries, LLC under the name H8035Power Meter. Unfortunately, it is burdensome to interconnect asignificant number of power meters and in particular the voltageconnections to the wires, especially if an interconnection to the wiresare not readily available. In addition, it is burdensome to interconnectthe output of the power meters, if any, to a computer network because ofthe need to provide communication wiring or other wireless communicationchannels to each of the remotely located power meters. Also, installingthe power meters requires significant expense for the technician tolocate a suitable location near each device, in addition to the furtherexpense of servicing the installed power meters.

[0004] What is desired, therefore, is an effective power monitoringsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 illustrates a power panel with circuit breakers.

[0006]FIG. 2 illustrates circuit breakers, associated sensors, and apower monitor.

[0007]FIG. 3 illustrates a perspective view of an exemplary embodimentof a support for a set of current sensors.

[0008]FIG. 4 illustrates a side view of the support and sensors of FIG.3.

[0009]FIG. 5 illustrates a top view of the support and sensors of FIG.3.

[0010]FIG. 6 illustrates a top view of the support and sensors of FIG. 2together with circuit breakers.

[0011]FIG. 7 illustrates a power panel assembly with a power monitor andthe support/current sensors of FIG. 3.

[0012]FIG. 8 illustrates a perspective view of another exemplaryembodiment of a support for a set of current sensors.

[0013]FIG. 9 illustrates a side view of the support and sensors of FIG.9.

[0014]FIG. 10 illustrates a top view of the support and sensors of FIG.9.

[0015]FIG. 11 illustrates the configuration of the current sensors andvoltage sensing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The present inventors reflected on the aforementioned limitationsinherent to using multiple independent power meters for a set of loadsand came to the realization that a power panel 10 provides a centralizedlocation where the currents in the wires to several different loads maybe sensed and the voltage in the bus bars that correspond with thecurrents may be sensed, with both being readily available. Moreover,unlike traditionally accepted power meters including multiple currentsensors and multiple voltage connections for each load to be measured,the present inventors came to the realization that the power providedfrom the bus bars to multiple different loads has the same voltagepotential and phase relationship with respect to each of the differentloads. In other words the power factor, which is a phase relationshipbetween the voltage and current provided to a load, may be determinedbased on the current to the particular load and the voltage in therespective bus bar. For a plurality of different loads the relationshipbetween the respective currents/voltages and power factor may bedetermined using the same bus bars. This commonality of voltages amongdifferent loads may be used as the basis to simplify the powermonitoring system. In particular, the power monitoring system may besubstantially improved by sensing the voltage potential together withits phase from each of the bus bars, preferably using one and only oneelectrical interconnection for each phase. The voltage potentialtogether with its phase relationship sensed from one or more bus barsmay be used together with the respective sensed currents provided to thedifferent loads to determine the instantaneous power usage and powerconsumed over a period of time for any particular load. In this manner,only a single interconnection for sensing the voltage potential isnecessary for each phase for multiple loads, each of which may have oneor more associated current sensors. The use of a single interconnectionfor sensing the voltage of each phase for multiple different loadsdecreases the time for installation, the expensive of the powermonitoring system, and decreases the likelihood of inadvertentlymis-connecting the voltage sensing connections. The use of a generallycentralized location for sensing the voltage and current for severaldifferent loads potentially permits easier installation of the powermonitoring system to a computer network for subsequent processing.Moreover, the centralized location reduces the technicians expense oflocating suitable locations for the power meter for a particular load.Further, the servicing of the power meters is more readily done becauseof their proximity to one another.

[0017] Referring to FIG. 2, to monitor the power provided to aparticular load from one or more individual circuit breakers 16 arespective current sensor 20 may be interconnected to the wire on theload side of the respective circuit breaker 16. Typical circuit breakersmay include a single phase, two phases, or three phases. The outputs 22of each of the current sensors 20 may be interconnected to a powermonitor 24. The current sensors 20 may be interconnected to one or morepower monitors. Also, the current sensors 20 may likewise be daisychained together, or interconnected to the power monitor(s) in any othersuitable manner. An electrical interconnection from each bus bar to thepower monitor(s) normally includes wires 23 a, 23 b, , 23 c, to sensethe voltage and its corresponding phase relationship. Alternatively, thevoltage potential and phase relationship for each phase may be sensedfrom locations other than the bus bars 14 a, 14 b, and 14 c, such as forexample, a wire provided to a load, the load side of a circuit breaker,the utility side of a circuit breaker, a capacitive coupling to thevoltage potential, or the wire connection from the utility. It is to beunderstood that the power monitor may calculate power based upon asingle phase, two phases, and/or three phases, etc., as desired. Inessence, the power monitoring system may use the electrical path fromthe power monitor 24 to the bus bars (or otherwise) of at least one ofthe phases for a plurality of different loads. Typically, the power iscalculated by multiplying the voltage, corresponding current, andcorresponding power factor which relates to the phase relationshipbetween the voltage and current.

[0018] It takes considerable time to install, at significant expense,all of the current sensors 20 and the available space within the powerpanel 10 may be insufficient for the desired number of current sensors.Also, the limited space available along the circuit breakers 16 mayresult in significant difficulty installing the current sensors 20, thusrequiring lateral spacing of the current sensors and bending the wiresfrom the circuit breakers to different locations within the power panel10 in an attempt to locate sufficient available space for the currentsensors 20. In addition, the large number of wires 22 from the currentsensors 20 to the power monitor 24 may require considerable space withinthe power panel 10. Further, because of the significant number ofindividual wires 22 an installer has a significant tendency tointerconnect the wires 22 to improper places within the power currentmonitor 24 and in particular to mismatch pairs of wires 22 from the samecurrent sensor 20 rending the current sensors 20 ineffective. Moreover,it is problematic to ensure that the wires 22 indicated by the installerthat relate to a particular current sensor 20 actually areinterconnected to the desired current sensor 20. In summary, thepotential installation problems are significant, especially when installby untrained technicians.

[0019] Referring to FIG. 3, a set of sensors 60 may be supported by asupport 62 which maintains the current sensors 60 in a fixed spatialrelationship with respect to one another. Preferably the support 62 isrigid or semi-rigid, while a flexible support 62 that was installed on arigid or a semi-rigid supporting member(s) may likewise be used. Thesensors 60 are preferably current sensors, or alternatively, other typesof sensors may be used. The sensors 60 are preferably wire woundtorodial coils on a metallic or non-metallic core enclosed within aplastic housing through which a wire 63 may be extended, and thehousings are at least partially surrounding the respective coil.Changing current within the wire 63 induces a changing magnetic fieldaround the wire 63. The changing magnetic field in turn induces achanging current within the wire wound torodial coil. The changingcurrent within the torodial coil may be used directly or converted toany suitable signal, such as for example, a voltage signal, or adifferent current signal.

[0020] The openings 64 defined by the sensors 60 are preferably orientedin a substantially parallel relationship with respect to each otherand/or oriented in a substantially perpendicular relationship withrespect to the longitudinal axis 66 of the support 62 or otherwise thegeneral alignment of the sensors. Preferably, one set of the alignedsensors have a first linear arrangement and another set of the alignedsensors have a second linear arrangement, which may be parallel to eachother. Also, preferably at least two of the aligned sensors have a firstlinear arrangement and at least two others of the aligned sensors have asecond linear arrangement. A single aligned set of sensors 60 may beused or more than two sets of sensors 60 may be used, as desired.

[0021] Referring also to FIG. 4, the sensors 60 may be arranged suchthat the housings surrounding the current sensors have an overlappingregion 70 in a substantially perpendicular direction with respect to thelongitudinal axis of the support 62 and/or general alignment of thesensors. Preferably, the openings 64 defined by the sensors 60 are in anon-overlapping relationship 72 with respect to one another and anon-overlapping relationship 74 with respect to other housings. Thispermits the sensors to be arranged in a more compact arrangement withinthe power panel.

[0022] Referring also to FIG. 5, a respective transient voltagesuppressor 80 may be interconnected in parallel across the outputterminals of each sensor 60. The transient voltage suppressors 80 limitsthe voltage build up at the terminals of the sensors 60, which may occurif the sensors are sensing a changing magnetic field while the terminalsof the sensors 60 are open circuited. This decreases the likelihood thattechnicians will be the recipient of an unanticipated electrical shock.

[0023] Referring to FIG. 6, the current sensors 60 are preferablyarranged in a spatial arrangement such that the openings 64 defined bythe current sensors 60 are in a substantially directly opposingrelationship with respect to the circuit breakers 16. In other words,the each of the openings 64 is opposing a respective circuit breaker 16.In this manner, the wires from the circuit breakers 16 may be readilyrouted through a respective sensor 60.

[0024] Referring to FIG. 7, during normal installation the support 62 isinitially affixed within the power panel in an adjacent spaced apartrelationship with respect to a set of circuit breakers 16. A support maybe located on both sides of a set of circuit breakers 16, if desired.Another support is illustrated in FIGS. 8, 9, and 10 suitable for theright hand side of the circuit breakers (FIGS. 3, 4, and 5 are suitablefor the left hand side). Then, the wires from the loads are passedthrough the respective sensors and interconnected to a respectivecircuit breaker 16. In addition, the wires 23 a, 23 b, and 23 c, forsensing the voltage potentials on the bus bars are likewise electricallyinterconnected. In this manner, the installation of the circuit breakersand the power monitor is efficient, less expensive, economical, and thesensors are in a suitable position with respect to the respectivecircuit breakers. The support 62 may be suitable for supporting a set ofelectrical traces that interconnect the sensors 60 to a connector 82.The interconnection from the sensors 60 to the connector 82 arepredetermined so that the signals provided to the connector 82 arereadily identifiable to the proper sensor 60. This eliminates thepotential possibility of improperly interconnecting the wires from thesensors 60 to the connector. A cable 84 interconnects each connector 82to a power monitor 24. While such a set of supports 62 with respectivesensors 60 are suitable for use with new installation, it is difficultto install such a set of sensors 60 to an existing set of circuitbreakers with wires already installed. To permit the sensors 60 to bereadily interconnected with wires already interconnected to the circuitbreakers 16 the sensors 60 may be constructed in a split-core manner. Inthis manner, the opening 64 may be opened, the wire inserted therein,and the opening 64 closed around substantially all of the wire.

[0025] To provide effective monitoring of the power usage used by theloads, the power monitor 24 may monitor the current levels of each ofcircuit breakers 16 together with the associated voltage potential andphase relationship.

[0026] The power monitor 24 may likewise be used to monitor the loadbalance between the different phases of the power panel 10. Frequently,the circuit breakers may be interconnected to a single phase when theloads require 120 volts, interconnected to two phases when the loadsrequire 240 volts, and interconnected to three phases when the loadsrequire three phase power. For example, the first phase of the powerpanel 10 may be supplying 70 amps, the second phase of the power panel10 may be supplying 30 amps, and the third phase of the power panel 10may be supplying 150 amps. This significant imbalance in the currentsupplied by the different phases is sub-optimal. For example, thegreater the current levels the greater the voltage drop from the powersource to the power panel, which may result in significant variations inthe voltage levels provided to the power panel from the three phasepower source. By monitoring the current (or power) provided from eachphase using the sensors, the loads may be redistributed between thedifferent phases to re-balance the loads.

[0027] In an alternative embodiment the power factor for one or morephases may be presumed to be a constant value. The power factor(normally the cosine of the phase difference) may be based uponhistorical measurements, test measurements, anticipated power factor,desired power factor, or otherwise omitted from the calculation of powerusage (equivalent to using a power factor of “1”).

[0028] In an alternative embodiment the power factor, the voltagepotential, and/or the current may be calculated, sensed, or otherwisemeasured for a single phase of a multi-phase load. The power monitor maythen use the voltage potential and current, together with the powerfactor if desired, to calculate the power usage of a multi-phase load bypresuming that the remaining phases have similar characteristics. Forexample, in a three phase system the remaining phases may be presumed tohave approximately a 60 degree phase difference. Reusing powercalculations for other phases reduces the computation complexity of thepower monitor while maintaining relatively accurate power measurements.

[0029] In an alternative embodiment, the power factor of a multi-phaseload may be determined based upon one of the voltages and one of thecurrents, both of which are preferably associated with the same phase.The power factor may then be used for all of the phases, if desired.Reusing the calculated power factor reduces the computational complexityof the power monitor while maintaining relatively accurate powermeasurements.

[0030] In an alternative embodiment, the power monitor may, if desired,separate multiple summed alternating voltage signals into theirrespective phases for power determination, typically by decomposition ofthe composite signal.

[0031] In an alternative embodiment, multiple electricalinterconnections may be provided from the power monitor to each of themultiple bus bars or otherwise the voltage potentials of the differentphases. Preferably, at least one of the electrical interconnections fromthe power monitor to at least one of the multiple bus bars, or otherwisethe voltage potential of at least one phase, is used together withdifferent current sensors for a plurality of different loads.

[0032] In an alternative embodiment, all or a portion of the powermonitoring system may be located outside of the power panel.

[0033] Referring to FIG. 11 in an alternative embodiment, it may bedesirable have the power monitor configurable to select which currentsensors correspond to the same load. In addition, the current sensorsmay be associated with the corresponding sensed voltage. Also, the phaserelationship of the current sensors and voltages may be indicated ifmore than one phase is provided to the load. The use of the currents andvoltages, together with the power factor if appropriate, may be used todetermine the power usage. The configuration may likewise enable anddisable the use of the power factor, if desired. Also, informationregarding other phases that are not available may be calculated by thepower monitor based upon the other phases. In addition, the power factorand/or voltage may be preset, if desired.

[0034] The terms and expressions which have been employed in theforegoing specification are used therein as terms of description and notof limitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. A power monitoring system comprising: (a) a first current sensorsuitable to sense changing electrical energy within a first conductor toa first load, said first current sensor providing a first signal; (b) asecond current sensor suitable to sense changing electrical energy witha second conductor to a second load, said second current sensorproviding a second signal (c) a first conductor sensing a first voltagepotential provided to said first load and to said second load; and (d) apower monitor that determines, (i) a first power measurement associatedwith said first load based upon, at least in part, said first signal andsaid first voltage potential; (ii) a second power measurement associatedwith said second load based upon, at least in part, said second signaland said first voltage potential.
 2. The system of claim 1 wherein saidfirst conductor is interconnected to a bus bar within a power panel. 3.The system of claim 1 wherein said first current sensor and said secondcurrent sensor include a wire wound torodial core.
 4. The system ofclaim 2 wherein said first conductor is an elongate wire.
 5. The systemof claim 1 wherein said power monitor further determines (a) a firstphase relationship between said first signal and said first voltagepotential; (b) a second phase relationship between said second signaland said first voltage potential; and (c) wherein said first phaserelationship is used in said determining said first power measurementand said second phase relationship is used in said determining saidsecond power measurement.
 6. The system of claim 1 further comprising:(a) a third current sensor suitable to sense changing electrical energywithin a third conductor to said first load, said third current sensorproviding a third signal; (b) a second conductor sensing a secondvoltage potential provided to said first load; and (c) wherein saidfirst power measurement is further based upon, at least in part, saidthird signal and said second voltage potential.
 7. The system of claim 6further comprising: (a) a fourth current sensor suitable to sensechanging electrical energy within a fourth conductor to said first load,said fourth current sensor providing a fourth signal; (b) a thirdconductor sensing a third voltage potential provided to said first load;and (c) wherein said first power measurement is further based upon, atleast in part, said fourth signal and said third voltage potential. 8.The system of claim 7 wherein said power monitor further determines (a)a first phase relationship between said first signal and said firstvoltage potential; (b) a second phase relationship between said secondsignal and said first voltage potential; and (c) wherein said firstphase relationship is used in said determining said first powermeasurement and said second phase relationship is used in saiddetermining said second power measurement.
 9. The system of claim 8wherein said power monitor further determines (a) a third phaserelationship between said third signal and said second voltagepotential; (c) wherein said third phase relationship is used in saiddetermining said first power measurement.
 10. The system of claim 9wherein said power monitor further determines (a) a fourth phaserelationship between said fourth signal and said third voltagepotential; (c) wherein said fourth phase relationship is used in saiddetermining said first power measurement.
 11. The system of claim 1wherein said first power measurement is an instantaneous powermeasurement.
 12. The system of claim 1 wherein said first powermeasurement is a power measurement for a period of time.
 13. The systemof claim 1 wherein said first conductor is the only interconnectionbetween said power monitor and said voltage potential.
 14. The system ofclaim 6 wherein said first conductor is the only interconnection betweensaid power monitor and said first voltage potential, and said secondconductor is the only interconnection between said power monitor andsaid second voltage potential.
 15. The system of claim 7 wherein saidfirst conductor is the only interconnection between said power monitorand said first voltage potential, and said second conductor is the onlyinterconnection between said power monitor and said second voltagepotential, and said third conductor is the only interconnection betweensaid power monitor and said third voltage potential.
 16. The system ofclaim 15 wherein said power monitor, said first current sensor, saidsecond current sensor, said third current sensor, said fourth currentsensor, said first conductor, said second conductor, and said thirdconductor, are enclosed within a power panel.
 17. The system of claim 16wherein a plurality of circuit breakers are included within said powerpanel.
 18. The system of claim 1 further comprising: (a) a support; (b)a third current sensor and a fourth current sensor, said first, second,third, and fourth current sensors defining an opening through which awire may be extended; and (c) said first, second, third, and fourthcurrent sensors being supported by said support in a fixed spatialrelationship.
 19. The system of claim 18 wherein said openings of saidfirst, second, third, and fourth sensors are oriented in a substantiallyparallel relationship with respect to each other.
 20. The system ofclaim 18 wherein said support has a longitudinal axis and said openingsof said first, second, third, and fourth sensors are substantiallyperpendicular to said longitudinal axis of said support.
 21. The systemof claim 18 wherein said openings of said first, second, third, andfourth sensors are oriented in a substantially perpendicularrelationship with respect to the general alignment of said first,second, third, and fourth sensors.
 22. The system of claim 18 whereinsaid first, second, third, and fourth sensors are aligned in only onesubstantially linear arrangement.
 23. The system of claim 18 whereinsaid first, second, third, and fourth sensors are aligned in at leasttwo substantially co-linear arrangements.
 24. The system of claim 23wherein at least two of said aligned first, second, third, and fourthsensors have a first linear arrangement and at least two others of saidfirst, second, third, and fourth aligned sensors have a second lineararrangement.
 25. The system of claim 18 wherein each of said first,second, third, and fourth sensors are maintained in a spatialarrangement opposed to respective circuit breakers.
 26. The system ofclaim 18 wherein said first, second, third, and fourth sensors arearranged such that a respective housing at least partially surroundingeach of said first, second, third, and fourth sensors has an overlappingregion in a substantially perpendicular direction with respect to atleast one of a longitudinal axis of said support and the generalalignment of said first, second, third, and fourth sensors.
 27. Thesystem of claim 18 wherein said openings of said first, second, third,and fourth sensors are arranged in a non-overlapping relationship withrespect to other said openings in a substantially perpendiculardirection with respect to at least one of a longitudinal axis of saidsupport and the general alignment of said first, second, third, andfourth sensors.
 28. The system of claim 18 wherein said openings of saidfirst, second, third, and fourth sensors are arranged in anon-overlapping relationship with respect to respective housings atleast partially surrounding each of said first, second, third, andfourth sensors in a substantially perpendicular direction with respectto at least one of a longitudinal axis of said support and the generalalignment of said first, second, third, and fourth sensors.
 29. Thesystem of claim 18 further comprising (a) a power panel; (b) a pluralityof circuit breakers within said power panel; (c) said power monitorwithin said power panel; and (d) said first, second, third, and fourthsensors arranged in a spatial arrangement such that said openingsdefined by said first, second, third, and fourth sensors are in asubstantially directly opposing relationship with respect to respectiveones of said circuit breakers.
 30. The system of claim 18 wherein saidfirst, second, third, and fourth sensors are split core first, second,third, and fourth sensors.
 31. An electrical sensing device comprising:(a) a support; (b) at least four sensors defining an opening throughwhich a wire may be extended; and (c) said sensors being supported bysaid support in a fixed spatial relationship.
 32. The device of claim 31wherein each of said sensors includes a wire wound torodial core. 33.The device of claim 31 wherein said openings of said sensors areoriented in a substantially parallel relationship with respect to eachother.
 34. The device of claim 31 wherein said support has alongitudinal axis and said openings of said sensors are substantiallyperpendicular to said longitudinal axis of said support.
 35. The deviceof claim 31 wherein said openings of said sensors are oriented in asubstantially perpendicular relationship with respect to the generalalignment of said sensors.
 36. The device of claim 31 wherein saidsensors are aligned in only one substantially linear arrangement. 37.The device of claim 31 wherein said sensors are aligned in at least twosubstantially co-linear arrangements.
 38. The device of claim 37 whereinat least two of said aligned sensors have a first linear arrangement andat least two others of said aligned sensors have a second lineararrangement.
 39. The device of claim 31 wherein each of said sensors aremaintained in a spatial arrangement opposed to respective circuitbreakers.
 40. The device of claim 31 wherein said sensors are arrangedsuch that a respective housing at least partially surrounding each ofsaid sensors has an overlapping region in a substantially perpendiculardirection with respect to at least one of a longitudinal axis of saidsupport and the general alignment of said sensors.
 41. The device ofclaim 31 wherein said openings of said sensors are arranged in anon-overlapping relationship with respect to other said openings in asubstantially perpendicular direction with respect to at least one of alongitudinal axis of said support and the general alignment of saidsensors.
 42. The device of claim 31 wherein said openings of saidsensors are arranged in a non-overlapping relationship with respect torespective housings at least partially surrounding each of said sensorsin a substantially perpendicular direction with respect to at least oneof a longitudinal axis of said support and the general alignment of saidsensors.
 43. The device of claim 31 further comprising (a) a powerpanel; (b) a plurality of circuit breakers within said power panel; (c)said device within said power panel; and (d) said sensors arranged in aspatial arrangement such that said openings defined by said sensors arein a substantially directly opposing relationship with respect torespective ones of said circuit breakers.
 44. The device of claim 31wherein said sensors are split core sensors.
 45. The device of claim 31further comprising (a) a connector supported by said support; and (b) apower monitor that receives a signal from said connector representativeof the current levels of a wire sensed by one of said sensors.
 46. Thedevice of claim 15 wherein said power monitor estimates the powerprovided by said wire.